988368

1. Introduction
Among all team sports, soccer is one of the most exciting and renowned fields all around the world. There are currently more than 265 million soccer players worldwide, and the number of participants, especially female players, is growing rapidly. Fifty-eight percent of soccer players are under the age of 18 years, and almost three-quarters of the players, following this field are young individuals under the age of 14 years [1]. Anterior cruciate ligament (ACL) risk of injuries is not only one of the most devastating lesions in youth soccer players but also lead to osteoarthritis in 80% of players aged under 15 years [2]. Also, 70% of ACL tears happen in non-contact mechanisms, and jump landing is one of the most common risky movement patterns leading to injury [3]. Shea et al. discovered that teenage girls and female soccer players had a greater prevalence of ACL injuries than did male players [4]. and the risk began between 10 and 12 years [5]. Children at this age often show dangerous maneuvers during landing activities [5, 6], comprising decreased knee flexion and increased knee valgus [7, 8], placing them at a higher ACL risk of injury. Krosshaug et al. investigated video records of 39 basketball players suffering ACL injuries. They estimated the injury time to be 17-50 ms after the initial contact with the ground. Both males and females reduced the bending angle of the knee at initial contact (<15) and 50 ms after (<28). The study also found that females had more knee flexion angles than males and that females were more prone to valgus collapse than males [9].
Proximal biomechanical defects may expose the knee to vulnerable positions and increase the likelihood of injury to the knee joint. The relationship between sub-optimal trunk position and hip and knee risk factors highlights the effect of trunk position on ACL injury. In addition, the collapse of the hip places the knee in the valgus position [8, 9]. Therefore, it can be said that trunk, hip, and knee mechanics have been supposed as key elements in the mechanism of ACL injury, particularly among females [10, 11]. Females demonstrate different neuromuscular control strategies than males during puberty. Puberty is accompanied by a sudden change in bone size and an increase in trunk volume. In males, this increase in volume has been related to an increase in neuromuscular control, muscle strength, and power. However, among females, the same increase in strength, power, and neuromuscular control does not occur [12]. 
According to the kinematic chain, the prior study suggested that knee kinematics were affected by proximal and distal joint motions [13, 14]. During jump landing, the peak valgus knee was connected to the peak hip adduction whereas the peak hip internal rotation angle was not [15]. Another study discovered that during a bilateral jump task, when ipsilateral trunk rotation occurred, valgus knee and internal rotation angle become greater, and the authors found that hip external rotation can be a logical justification for these findings [16]. Furthermore, a video evaluation study demonstrated that the hip internal rotation, flexion, and adduction angles did not alter during initial contact and could not lead to an ACL injury [17]. Considering the relationship between hip and trunk kinematics with the valgus knee in different tests, results may vary.
The kinematic relationships between the trunk and hip kinematics with knee abduction angle during landing remain uncertain among preadolescent females. Therefore, the study aimed to investigate the relation of the peak hip kinematic angles and peak trunk angles with peak knee abduction during single-leg landing among preadolescent female soccer players.

2. Materials and Methods
Participants 
In this study, 36 preadolescent female soccer players (Mean±SD age: 11.2±1.1 years, height: 148.4±5.4 cm, weight: 40.9±3.5 kg) participated. The inclusion criteria were healthy participants aged 10 to 12 years and playing football twice per week for at least six months. All testing procedures were explained to each athlete, and consent forms were signed by the participant or parents. Exclusion criteria were an injury history of knee ligaments or muscles of the lower extremities and impaired balance. It should be mentioned that the dominant leg of the whole athlete was the right limb and it had been tested and analyzed. 

Data collection
An 8-camera motion capture (Qualisys; Goteborg, Sweden) collected kinematic data at 200 Hz using a marker set in a calibration area. Forty-five reflecting markers were put on the body (C7 and T10, shoulders, scapula inferior angles, sacrum, anterior and posterior superior iliac spine, iliac crest, greater trochanter, knee, ankle, and second and fifth metatarsal heads, heels) based on a visual 3D marker set [18] and four clusters were placed on the thigh and shank. Participants warmed up for 5 minutes on a stationary bicycle and after that, they did a static trial and performed landing trials. A single-leg drop landing was applied to assess the landing kinematics (Figure 1).

The attendees received instructions to stand on non-leg dominance and then drop from a box with a height of 30 cm from the ground with leg dominance. Three successful trials of the single-leg landing were collected [19]. 

Data processing and statistical analysis 
The phase of landing was the interval between the initial contact to peak knee flexion. The positive angles indicate hip adduction and internal rotation. Kinematic data were collected using visual 3D.
Pearson correlation coefficient was used to measure relationships between the peak trunk and hip kinematics and peak knee abduction angle. The statistical process was analyzed using SPSS software, version 25. The Kolmogorov–Smirnov test was used to identify the normal distribution of the data. Statistical significance was met at the level of P≤0.05.

3. Results 
The means peak hip, trunk, and knee abduction kinematics data are reported in Table 1.

Pearson correlation coefficient showed a statistically significant positive relationship between peak hip internal rotation (r=0.361) (P=0.03) and peak knee abduction (Figure 2A).

Moreover, there was no significant relationship between peak hip adduction (r=-0.102) (P=0.55) (Figure 2B), peak trunk rotation (r=0.239) (P=0.16) (Figure 3C), peak trunk lateral flexion (r=0.052) (P=0.76), and knee abduction angle (Figure 3D) (Table 2).

4. Discussion
This study aimed to determine the relationship between hip kinematics and trunk kinematics and peak valgus knee among female preadolescent soccer players during single-leg drop landing. There was a weak correlation between these two parameters but a significant relationship was found between peak knee abduction and peak hip internal rotation. In a previous study, knee abduction motion was a major indicator of ACL lesions in female players, and a smaller knee abduction angle was especially crucial to decrease ACL injuries [14]. In another study, females showed greater hip internal rotations combined with a greater knee valgus during weight-bearing movements of single-leg compared to males, which may be mechanisms of ACL injury [20, 21, 22]. Furthermore, a risky kinematic relationship known as the dynamic valgus knee goes along with hip internal rotation, which may produce ACL injuries [23]. In the present study, even though large peak hip internal rotation kinematics may contribute to large peak knee abduction, and future studies should consider several combined factors, such as neuromuscular control of the hip and trunk to avoid ACL injuries. Also, because the study was performed during the COVID-19 pandemic, we applied a small number of participants, which affects the results of the study. 
Our study demonstrated that the peak hip adduction angle was not correlated with the peak knee abduction according to the Pearson correlation coefficient. The foot placed in maximum knee flexion and a hip adduction angle greater than 5° increased the ACL risk of injuries [24]. In the present study, during single-leg drop landing, preadolescent female soccer players possibly experienced considerable stress on the ACL in the dominant lower limb due to larger hip adduction and internal rotation as well as the combined dynamic valgus knee. However, we failed to find a significant correlation between peak hip adduction and peak knee abduction angles. During a single-leg task, a larger hip adduction angle but not a hip internal rotation angle was connected to a higher knee abduction angle [15]. The main reason for the difference is the type of tasks and the age of the subjects. Another remarkable point to be mentioned about this subject is that hip rotation is affected by the internal rotation of the tibia. To put it another way, when the tibia internal rotation happens with the hip external rotation with flexed knee, the knee abduction might be increased [16]. 
In the present study, preadolescent female soccer players landed with increased trunk lateral flexion, and rotation angles but no correlation was found between peak trunk rotation, lateral flexion angles, and peak knee abduction angle during single-leg drop landing. Nakagawa et al. reported that a large ipsilateral lateral trunk flexion was significantly related to higher knee abduction in healthy participants [25], which is inconsistent with the present study. Different tasks of assessing kinematics also lead to different results. When female athletes reach maturity, weak “core stability” may affect increased dynamic knee valgus during dynamic tasks [26]. It is stated that the development of poor movement patterns in early-pubertal females is because of an increase in height and weight, leading to more loading on ACL injuries [27]. Willy et al. reported that core strength training, including strengthened gluteal muscle exercises, can reduce ACL risk factors, like the valgus knee [28].
Additionally, higher hip external rotation and knee internal rotation angles may be associated with ipsilateral trunk rotation during bilateral jump tasks [16]. However, in the current investigation, the correlation between hip and knee rotations was disregarded. Next studies are essential to exhibit risky kinematic relationships among female soccer players in early puberty. In general, to control hip alignment properly, it is important to activate the contraction of hip external rotators eccentrically during landing [13]. Also, it was suggested that intervention programs to control knee abduction motion in early puberty may be an effective time during maturation [29]. 

5. Conclusion
This study investigated the relationship between hip kinematics and peak valgus knee in preadolescent soccer players. The Pearson correlation coefficient indicated that there is a kinematical connection between peak hip internal rotation angle and peak knee abduction with a weak correlation value. Therefore, kinematic risk factors related to ACL injuries in combination with neuromuscular control trunk and hip can be considered during more demanding tasks in future studies. Furthermore, the significant kinematic association of peak hip adduction, peak trunk rotation, and peak trunk lateral flexion with peak knee abduction angle was not determined. It is suggested that neuromuscular training to avoid a large knee abduction angle might be advantageous among female preadolescent soccer players. 
Some limitations should be considered in this study. First, to the identification of ACL injury mechanisms, other landing tasks, like double-leg jump and vertical drop jump should be evaluated. Only kinematic variables were analyzed. Future studies should include kinetic assessments. Moreover, only preadolescent female soccer players were included in the present study and the findings cannot be generalized to males or other athletes. 

Ethical Considerations
Compliance with ethical guidelines
The Local Ethics Committee (Ethical Code: IR.BASU.REC.1400.035) regarding the standards and guidelines of the Declaration of Helsinki confirmed and registered the study protocol.

Funding
This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors.

Authors' contributions
All authors equally contributed to preparing this article.

Conflict of interest
The authors declared no conflict of interest.

Acknowledgments
We would like to appreciate all players, parents, and coaches for cooperating with us in this study.


References

1. Kunz M. 270 million people active in football [Internet]. 2007 [Updated 2022 December 26]. Available from: [Link]
2. Lohmander LS, Östenberg A, Englund M, Roos H. High prevalence of knee osteoarthritis, pain, and functional limitations in female soccer players twelve years after anterior cruciate ligament injury. Arthritis & Rheumatology. 2004; 50(10):3145-52. [DOI:10.1002/art.20589] [PMID]
3. Ganapathy PK, Collins AT, Garrett WE. Mechanisms of noncontact anterior cruciate ligament injuries. The Anterior Cruciate Ligament. 2018; 43(4):16-9.e2. [DOI:10.1016/B978-0-323-38962-4.00004-7]

4. Shea KG, Pfeiffer R, Wang JH, Curtin M, Apel PJ. Anterior cruciate ligament injury in pediatric and adolescent soccer players: An analysis of insurance data. Journal of Pediatric Orthopaedics. 2004; 24(6):623-8. [DOI:10.1097/01241398-200411000-00005] [PMID]
5. Gianotti SM, Marshall SW, Hume PA, Bunt L. Incidence of anterior cruciate ligament injury and other knee ligament injuries: A national population-based study. Journal of Science and Medicine in Sport. 2009; 12(6):622-7. [DOI:10.1016/j.jsams.2008.07.005] [PMID]
6. Hass CJ, Schick EA, Tillman MD, Chow JW, Brunt D, Cauraugh JH. Knee biomechanics during landings: Comparison of pre- and postpubescent females. Medicine & Science in Sports & Exercise. 2005; 37(1):100-7. [DOI:10.1249/01.MSS.0000150085.07169.73] [PMID]
7. Swartz EE, Decoster LC, Russell PJ, Croce R V. Effects of developmental stage and sex on lower extremity kinematics and vertical ground reaction forces during landing. Journal of Science and Medicine in Sport. 2005; 40(1):9-14. [PMID] [PMCID]
8. Boden BP, Dean GS, Feagin JA Jr, Garrett WE Jr. Mechanisms of anterior cruciate ligament injury. Orthopedics. 2000; 23(6):573-8. [DOI:10.3928/0147-7447-20000601-15] [PMID]
9. Krosshaug T, Nakamae A, Boden BP, Engebretsen L, Smith G, Slauterbeck JR, et al. Mechanisms of anterior cruciate ligament injury in basketball: Video analysis of 39 cases. The American Journal of Sports Medicine. 2007; 35(3):359-67. [DOI:10.1177/0363546506293899] [PMID]
10. Willson JD, Ireland ML, Davis I. Core strenght and lower extremity alignment during single leg squats. Medicine & Science in Sports & Exercise. 2006; 38(5):945-52. [DOI:10.1249/01.mss.0000218140.05074.fa] [PMID]
11. Hollman JH, Ginos BE, Kozuchowski J, Vaughn AS, Krause DA, Youdas JW. Relationships between knee valgus, hip-muscle strength, and hip-muscle recruitment during a single-limb step-down. Journal of Sport Rehabilitation. 2009; 18(1):104-17. [DOI:10.1123/jsr.18.1.104] [PMID]
12. Hewett TE, Myer GD, Ford KR. Decrease in neuromuscular control about the knee with maturation in female athletes. The Journal of Bone and Joint Surgery. 2004; 86(8):1601-8. [DOI:10.2106/00004623-200408000-00001] [PMID]
13. Malloy PJ, Morgan AM, Meinerz CM, Geiser CF, Kipp K. Hip external rotator strength is associated with better dynamic control of the lower extremity during landing tasks. Journal of Strength & Conditioning Research. 2016; 30(1):2820291. [DOI:10.1519/JSC.0000000000001069] [PMID] [PMCID]
14. Hewett TE, Myer GD, Ford KR, Heidt RS, Colosimo AJ, McLean SG, et al. Biomechanical measures of neuromuscular control and valgus loading of the knee predict anterior cruciate ligament injury risk in female athletes: A prospective study. The American Journal of Sports Medicine. 2005; 33(4):492-501. [DOI:10.1177/0363546504269591] [PMID]
15. Hogg JA, Schmitz RJ, Shultz SJ. The Influence of hip structure on functional valgus collapse during a single-leg forward landing in females. Journal of Applied Biomechanics. 2019; 35(6):370-6. [DOI:10.1123/jab.2019-0069] [PMID]

16. Critchley ML, Davis DJ, Keener MM, Layer JS, Wilson MA, Zhu Q, et al. The effects of mid-flight whole-body and trunk rotation on landing mechanics: Implications for anterior cruciate ligament injuries. Sport Biomechanics. 2020; 19(4):421-37. [DOI:10.1080/14763141.2019.1595704] [PMID] [PMCID]
17. Koga H, Nakamae A, Shima Y, Iwasa J, Myklebust G, Engebretsen L, et al. Mechanisms for noncontact anterior cruciate ligament injuries: Knee joint kinematics in 10 injury situations from female team handball and basketball. The American Journal of Sports Medicine. 2010; 38(11):2218-25. [DOI:10.1177/0363546510373570] [PMID]
18. Yu B. Effect of external marker sets on between-day reproducibility of knee kinematics and kinetics in stair climbing and level walking. Research in Sports Medicine. 2003; 11(4):209-18. [DOI:10.1080/714041037] [PMID]
19. Thompson-Kolesar JA, Gatewood CT, Tran AA, Silder A, Shultz R, Delp SL, et al. Age influences biomechanical changes after participation in an anterior cruciate ligament injury prevention program. The American Journal of Sports Medicine. 2018; 46(3):598-606. [DOI:10.1177/0363546517744313] [PMID]
20. Ireland ML. Anterior cruciate ligament injury in female athletes: Epidemiology. Journal of Athletic Training. 1999; 34(2):150-4. [PMID] [PMCID]
21. Leetun DT, Ireland ML, Willson JD, Ballantyne BT, Davis IMC. Core stability measures as risk factors for lower extremity injury in athletes. Medicine & Science in Sports & Exercise. 2004; 36(6):926-34. [DOI:10.1249/01.MSS.0000128145.75199.C3] [PMID]
22. Ferber R, Davis IM, Williams DS. Gender differences in lower extremity mechanics during running. Clinical Biomechanics. 2003; 18(4):350-7. [DOI:10.1016/S0268-0033(03)00025-1] [PMID]
23. Hewett TE, Ford KR, Hoogenboom BJ. Invited clinical commentary understanding and preventing acl injuries: Considerations - update 2010. North American Journal of Sports Physical Therapy. 2010; 5(4):234-51. [PMID] [PMCID]
24. Sigward SM, Pollard CD, Havens KL, Powers CM. Influence of sex and maturation on knee mechanics during side-step cutting. Medicine & Science in Sports & Exercise. 2012; 44(8):1497-503. [DOI:10.1249/MSS.0b013e31824e8813] [PMID] [PMCID]
25. Nakagawa TH, Maciel CD, Serrão FV. Trunk biomechanics and its association with hip and knee kinematics in patients with and without patellofemoral pain. Manual Therapy. 2012; 20(1):189-93. [DOI:10.1016/j.math.2014.08.013] [PMID]
26. Myer GD, Chu DA, Brent JL, Hewett TE. Trunk and hip control neuromuscular training for the prevention of knee joint injury. Clinical Journal of Sport Medicine. 2008; 27(3):425-48. [DOI:10.1016/j.csm.2008.02.006] [PMID] [PMCID]
27. Otsuki R, Benoit D, Hirose N, Fukubayashi T. Effects of an injury prevention program on anterior cruciate ligament injury risk factors in adolescent females at different stages of maturation. Journal of Sports Science and Medicine. 2021; 20(2):365-72. [DOI:10.52082/jssm.2021.365] [PMID] [PMCID]
28. Willy RW, Davis IS. The effect of a hip-strengthening program on mechanics during running and during a single-leg squat. Journal of Orthopaedic & Sports Physical Therapy. 2011; 41(9):625-32. [DOI:10.2519/jospt.2011.3470] [PMID]
29. Ford KR, Shapiro R, Myer GD, Van Den Bogert AJ, Hewett TE. Longitudinal sex differences during landing in knee abduction in young athletes. Medicine & Science in Sports & Exercise. 2010; 42(10):1923-31. [DOI:10.1249/MSS.0b013e3181dc99b1] [PMID] [PMCID]